A conventional system for industrial and commercial refrigeration or air conditioning might employ ammonia, for example, as a refrigerant. The ammonia, in gaseous form, is compressed in a compressor, from which it is discharged at a higher temperature and pressure. The compressed refrigerant gas travels to a condenser where it is liquified at a lower temperature. Cooled liquid refrigerant then travels through evaporator coils where it performs its cooling or refrigeration function by removing heat from the surrounding environment through the coils.
The evaporator coils normally accumulate moisture and, accordingly, frost during operation. Periodically these evaporator coils have to be defrosted in order to maintain the efficiency of the system. There are four widely used methods of defrosting evaporator coils. These might be characterized as the air method, the water method, the electric method, and the hot gas method.
The hot gas defrost method is the most popular of the four. In the hot gas defrost method the supply of liquid refrigerant to the evaporator coil is interrupted and high pressure refrigerant vapor is delivered to the evaporator. While the high pressure refrigerant vapor is being delivered to the evaporator coil, the outlet of the coil is restricted so that a pressure is maintained in the coil. This provides a saturation temperature high enough to transfer heat to the frost or ice on the evaporator coils. As a result of this manipulation, the evaporator coil temporarily becomes a condenser coil. The latent heat given off into the frost during the condensation process is the major energy source for the defrost.
To begin the defrost cycle, a first solenoid valve downstream of the condenser is closed and a second solenoid valve in a bypass line which leads directly from upstream of the condenser to upstream of the evaporator is opened. These solenoid valves normally open and close rapidly. When the bypass line has some liquid in it in addition to the hot gas from the compressor (as is frequently the case) a "slug" of liquid or a liquid-gas mixture rapidly passes through the second solenoid valve and strikes downstream system components, including the evaporator. What is known as "hydraulic shock" occurs and, particularly where the system is operating at low temperatures, severe damage to the system can result.
A primary object of the invention is to provide an improved shockless, hot gas defrost refrigeration system for industrial and commercial refrigeration and air conditioning and the like.
It is another object to provide an improved refrigeration system wherein hydraulic shock damage to system components due to rapid opening of control valves is prevented.
Yet another object is to provide a refrigeration system wherein slug flow in the pipe line is prevented from rapidly moving downstream so as to cause hydraulic shock, a result potentially damaging to system components.
The foregoing and other objects are realized in accordance with the present invention by providing a slug surge suppressor device interposed in the gas line of a refrigeration system. The slug surge suppressor is advantageously placed downstream of the solenoid valve in the hot gas line, and also downstream of a pressure regulator valve which is downstream of the evaporator in a suction line.
In one aspect of the invention, the slug surge suppressor comprises a plurality of beads, fibers or other materials which act together to form numerous capillary passages. The beads are generally confined by first and second perforated screens. The numerous capillary passages resist liquid flow and lower liquid pressure, but allow gas to flow freely without a significant drop in gas pressure. The pressure drop in the liquid not only moderates (i.e., slows down) the slug surge, but also makes the liquid evaporate rapidly. Thus, slug surge is prevented.
In another aspect of the invention, the slug surge suppressor as described above further includes an alarm system and a third perforated screen located downstream of the second (downstream-most) perforated screen, and electrically insulted from the same. The alarm system is connected in such a way to detect breakage of the second screen and sound the alarm. The third screen confines the beads upon breakage of the second screen to prevent the beads from traveling downstream and causing damage to system components.
In another aspect of the invention, the slug surge suppressor includes a set of turbine-like blades which impart a tangential velocity to the liquid-gas slug. The tangential velocity and different densities of the liquid and gas causes each to flow along a different path. The gas will flow directly downstream to the outlet port through one passage which is directed toward the middle of the slug surge suppressor. The liquid will tend to swirl downstream along an innerwall of the slug surge suppressor body. The liquid then passes through a plurality of beads which act together to form numerous capillary passages which resist liquid flow by viscous effects and lower liquid pressure. The pressure drop in the liquid not only moderates the slug surge, but also makes the liquid evaporate rapidly. Thus, slug surge is prevented.
In yet another aspect of the invention, the slug surge suppressor utilizes a circular non-perforated plate to impart a tangential velocity to the liquid-gas slug. The tangential velocity and different densities of the liquid and gas causes each to flow through the slug surge suppressor along a different path in a manner similar to that described immediately above.